Intermediate frequency amplifier system



July 25, 1939. w. l.. cARLsoN INTERMEDIATE FREQUENCY AMPLIFIER SYSTEM 2Sheets-Sheet 1 Filed Dec. 18, 1937 Snnentor Gttorneg July 25, 1939. w. 1CARLSON 2,157,605

INTERMEDIATE FREQUENCY AMPLIFIER SYSTEM :7 l Filed Dec. 18, 1937 2Sheets-Sheet 2 zo-@Mc 65 7i Ffn/ /g 67 60 i u l ll 55 v -E E I mei/l -CLB B FWEQ. 77 d3 /57 E 72 Vi 9/ 73 i l i l Osc.

Low was@ 3nventor Bg I Gttorneg Patented July 25, 1939 UNITED STATESmTERMEDIATE FREQUENCY AMPLIFIER SYSTEM Wendell L. Carlson, Haddonleld,N. J., assignor to Radio Corporation ol' America, a corporation ofDelaware Application December 18, 1937, Serial No. 180,490

14 Claims.

'I'he present invention relates to an intermediate frequency amplifiersystem for radio receivers, and has for its primary object to provide animproved amplifier system of that character for multiple wave band radioreceiver systems having a frequency coverage in at least one ultra highfrequency band.

By way of example, the invention may be considered to relate Ito amultiple wave band receiver of the type covering a frequency range offrom substantially 500 to '70,000 kilocycles and divided into thepresent standard broadcast, medium short wave, short wave. and `ultrahigh frequency bands, which are commonly known at present as the A, B, Cand D bands, respectively, for broadcast receivers and the like, the Dor ultra high frequency band being in the range above 20,000 kilocycles.

It is a further object of the present invention to provide anintermediate frequency amplifier system which permits a frequencyresponse or channel width for the higher frequency bands greater thanthe present five kilocycle range on each side of resonance, and topermit the same to be extended to as wide as from 10 to 50 kilocycles oneach side of the resonant or main frequency response of the signalreceiving channel. With this arrangement, the intermediate frequencychannel may have a response characteristic which is from two to fivetimes as wide as is now used.

It is an object of the invention to provide covering the same number ofbroadcast or signal channels as in the present broadcast range, in awider frequency range corresponding to the increased band width of thereceiving system. For example, with the present broadcast tuning rangecovering substantially 1000 kilocycles, from 540 to 1600 kilocycles, itis proposed that an ultra high frequency tuning range cover at least2000 kilocycles, for example, between 40 and 42 megacycles. With thesame number of channels for an even wider band width of the responsecharacteristic of the tuning system, the ultra high frequency or D bandrange may cover from 20,000 to 60,000 kilocycles.

It is also an object of the present invention to provide an improvedintermediate frequency amplfier system for a multiple wave band receiverhaving an ultra high frequency band, with two intermediate frequencychannels responsive to different intermediate frequencies so related andseparated that a harmonic of the lowerintermediate frequency does notfall within the response range of the higher intermediate fre- (ci. o-20) quency amplifier channel, whereby the same amplifier tubes andcircuits may be used for both channels and the switching from onechannel to another may be effected in a simple manner.

It is also a further object of the present invention to provide animproved intermediate frequency amplifier system for a multiple waveband receiver having a high intermediate frequency amplifier channeldesigned to pass double side band modulation frequencies-in a band widthseveral times as wide as used for a low intermediate frequency amplifierchannel in the same system, whereby in the higher frequency'tuning bandshigher fidelity of reproduction may be obtained, a higher image ratiomay be provided, less acoustic feedback is encountered, and there isless tendency for signals to drift out of tune.

In carrying out the invention, a low intermediate frequency ampliferchannel is provided for the A, B and C bands, while a separate highfrequency intermediate amplifier is provided for the D or high frequencytuning band and may be used for the C band, if this is also in arelatively high frequency range. The switching from the low intermediatefrequency channel to the high intermediate frequency channel is effectedby a simple switching arrangement preferably in conjunction with theband change control means.

It has been found that it is sometimes desirable to change 'thefrequency converter, including the type of oscillator Aused forreceiving signals in differing frequency bands, that is, one type ofoscillator and converter is more effective and stable at ultra highfrequencies, while another type of oscillator and converter may producea uniform signal output over the tuning range of another signalreceiving band.

Accordingly, it is an object of the present invention to provide animproved intermediate frequency amplifier system wherein the twoamplifier channels may be provided as hereinbefore referred to, and mayinclude different frequency converters and oscillators in conjunctionwith each channel, arranged selectively to be rendered effective bysimple switching means, and effectively coupled to the respectiveamplifier channels with which they operate.

The invention, however, will be better understood from the followingdescription, when considered in connection with the accompanyingdrawings, and its scope will be pointed out in the appended claims.

In the drawings, Figure 1 is a schematic circuit diagram of a multiplewave band radio receiving system embodying the invention;

Figure 2 is a curve showing the relative response characteristic betweentwo amplifying channels in the circuit of Fig. l;

Figure 3 is a schematic circuit diagram of a portion of the circuitshown in Fig. 1 and embodying the invention; and

Figure iis a further schematic diagram of a radio receiving systemembodying the invention, and providing a further modification of thesystem shown in Fig. 1.

Referring to Fig. 1, the radio receiving system shown may comprise anysuitable multiple wave band tuner and oscillator, as indicated at 5.having a tuning indicator 6 and a tuning control means 1, whereby it istunable through each of the various wave bands selectable by a bandchange control means indicated at 3. This band change control may beassumed to cover the usual number of wave bands, such as the A, B, C andD bands referred to hereinbefore.

The tuning means and oscillator are coupled to a converter or frequencychanger comprising a multiple grid tube 8, having a grid I0 forreceiving oscillations and a grid II for receiving the incoming signal,whereby the oscillations and signal are mixed at the output circuitindicated at I2. The output circuit I2 is the output anode circuit ofthe mixer tube 9 in the present example, and this is arranged to beselectively connectable to either one of two amplifying channelsindicated at I3 and Il, both of which are arranged to use commonamplifier tubes indicated at I5 and' I6 and a common rectifier ordetector indicated at I'l.

In providing the circuit and tube arrangement referred to, the ampliierchannel I3 is provided with interstage tuned coupling transformers I8,I9 and 20, all tuned to the same intermediate frequency, which may be ahigh intermediate frequency such as 2500 kilocycles, for example, whilethe channel I4 includes corresponding interstage coupling transformersindicated at 2|, 22, and 23, tuned to the same low intermediatefrequency, such as 460 kilocycles, for example.

The circuit arrangement 0f the amplier is such that, from the convertertube 9, the intermediate frequency signal passes through the outputcircuit I2 to a simple two-point switch indicated at 25 and selectivelythrough the switch to the tuned primary 26 of the transformer I8 or tothe tuned primary 2l of thetransformer 2| ,thetwo primaries being tunedto 2500 kilocycles and 460 kilocycles, respectively. The tunedsecondaries 28 and 29, respectively, of the transformers I8 and ZI areconnected permanently in series between the input grid 30 of the rstamplier tube I5 and the cathode circuit 3I through a suitable biaspotential source indicated at 32. Each of the pn'- maries may beconnected to a suitable B potential source, as indicated.

The remaining secondaries of the other interstage coupling transformersIS-ZZ and 20--23 are similarly connected with the succeeding tubes i6and I'l and the primaries of the said transformers are likewiseconnected in series as indicated so that, between the successive tubesof the amplifier, the primaries and secondaries of the interstagecoupling means are connected in series and are rendered effective tocouple the amplier tubes in cascade relation to each other as anintermediate frequency ampliiier responsive to two intermediatefrequencies or narrow bands of frequencies about two mean widelyseparated intermediate frequencies.

The secondaries 28 and 28 are tuned respectively to the frequencies oftheir corresponding primary winding and, together, form an input circuitfor the first amplifier tube which passes two bands of frequencies, thatis, the amplifier is a double frequency amplifier with only oneintermediate frequency signal impressed on the amplifier at a giventime, determined by the position of the switch means 25, which may becoupled to the band change control, as indicated by the dottedconnecting line 35. In a four-band tuning system of the type referredto, the connection is such that the switch means 25 is moved from anoutput connection with the'low frequency channel I4 to the connectionshown with the high frequency channel I3, when the band change controlis moved to provide tuning in the highest frequency range, such as the Dband, and even in both the C and D bands,if the C band is arranged toinclude relatively high frequencies, such as frequencies above 20,000kilocycles, for example.

Each of the succeeding amplifier stages and the detector I'I aresimilarly coupled for response in the two frequency bands orintermediate frequencies, the low frequency channel I4 being responsivein a narrower band about the 460 kilocycle mean frequency and thechannel I3 being responsive in a broad band about the 25,000 kilocyclemean frequency, whereby high fidelity operation is obtained in the highfrequency channel.

The channel I3 may be made responsive to a high intermediate frequency,for example, of 4000 kilocycles. However, it is desirable that with theremaining amplifier stages and detector permanently coupled by theseries connection between the two channel coupling means, the relationbetween the two intermediate frequencies be such that the harmonic ofthe lower intermediate frequency does not fall within the present rangeof the higher intermediate frequency amplier.

The relative frequency response of the two channels is indicated in Fig.2, to which attention is now directed, along with Fig. l, and in whichthe response peak at 38 is the characteristic response of the amplifierchannel I 4, while the response peak at 39 is that of the amplifierchannel I3. The 460 kc. peak may have a band width of, for example, 5 or10 kilocycles at or near resonance, and the 2500 kc. peak may have aband width, for example, of 10 or 20 kilocycles at or near resonance.The several transformers LC ratios may be so proportioned as to amplifyequally through the various stages at both frequencies or the design maybe arranged so as to increase the amplification of one channel more thanthe other.

With this response characteristic and spacing of the two frequencies ofthe amplifier, the switching between the two channels may be effected bythe simple switching means in connection with the separate primarywindings 0f the initial or input coupling transformers of each channel,as shown. If desired, the switching means may be extended to include thesecondary windings as well as the primary windings of transformers I8and 2I. The transformers are preferably tuned by movable magnetic coresin connection with fixed capacitors, as indicated.

It will be noted that the interstage coupling transformers for the twochannels in the inter* mediate frequency amplifier are arranged in sucha manner, serially in circuit with the tubes, that the high frequencychannel coupling transformers are connected in circuit adjacent to thetube plate and grid elements, whereby they are located at the highpotential ends of the input and output circuits for the various tubes,while the low frequency channel coupling elements are located in the lowpotential sides of the responsive input and output circuits for thetubes and more adjacent to the cathode and plate supply for therespective grid and plate circuits. The transformers I8 and 2| may be ina common shield container or in separate containers. This also appliesto transformers I9 and 22 and t0 transformers 20 and 23.

In order to place the simple switching arrangement involving a two-pointswitching change more adjacent to the low potential side of the inputcoupling means of the amplifier, and thereby avoid regeneration due tocapacity coupling between the switch and other parts of the amplifiersystem, the circuit shown in Fig. 3 may be used between the converter 9and the first amplifier tube I5.

Referring to Fig. 3, the output circuit I2 is connected permanently to alow frequency tuned primary winding 40 and a high frequency tunedprimary 4I in series, while the input grid 30 of the tube I5 isconnected permanently to a high frequency tuned secondary winding 42 anda low frequency tuned secondary winding 43 in series. The primarywinding48 is coupled to the secondary winding 43, while the primary winding 4Iis coupled to the secondary winding 42, as indicated.

`The two transformers thus provided are electrostatically andelectromagnetically separated by space or by suitable shielding means,as indicated at 44. It is important that 460 kc. signals be highlyattenuated when the switch is set for reception of 2500 kc. signals.Likewise, 2500 kc. signals must be highly attenuated when the switch isset for reception of 460 kc. signals. Therefore, coupling between coils48 and 42 should be avoided.

In this input coupling circuit, the switching for selecting the twochannels is provided at the low potential or anode supply end of theprimary circuit and at the bias or low potential side of the secondarycircuit, by a selector switch means having one section indicated at 45which may be closed, as shown, when the other section, indicated at 46,is open, and when the section 46 is closed the section 45 opens. 'I'heswitch sections are utilized to connect in circuit the tuning capacitorsfor the primary winding 4I and the secondary winding 43, as indicated at41 and 48, respectively.

When the switch section 46 is closed, the high frequency primary 4I istuned to apply energy to the tuned secondary 42 at 2500 kilocycles, andthe tuned secondary winding 43 is rendered ineffective to respond in the460 kilocycle range because of the opening of the switch section 45.which disconnects the tuning capacitor 48.

When the switch section 45 is closed, the secondary winding 43 is tunedto respond to signals in the 460 kilocycle range, and receives energy.from the low frequency primary 40. Since the switch section 46 in thenopen, the primary 4I is untuned and is rendered ineffective to transferenergy to the secondary 42. In switching the low frequency secondarywinding 43, it will be seen that the winding is open-circuited by theswitch section 45, and this is desirable in reducing the response fromthis winding when operating the amplifier in the high frequency range.In order to supply biasing potential to the grid 30 when the winding 43is open-circuited, a bias supply resistor is provided, as indicated at49. to complete the grid circuit around the capacitor 4I. This is arelatively high resistance and provides no appreciable load on thecapacitor while at the same time conveying the biasing potential to thegrid 38.

0n the primary side, anode current is permitted to flow through theuntuned winding 4I when the switch section 46 is opened. Both switchsections 45 and 46 are connected to operate alternately in connectionwith the band change means, as indicated by the dotted connections 50.

From the foregoing description, it will be seen that for an al1-wavereceiver of the superheterodyne type, a double intermediate frequencyamplifier may be provided with one intermediate frequency signal passingtherethrough at a given time, and selective control may be provided by asimple two-position switch coupled to the band change means, to operatewhen the band change means is-moved to provide ltuning in the ultra highfrequency or D band. Furthermore, it will be seen that switching may beprovided at low intermediate frequency potentials, so that the switchmeans has no substantially high potentials thereon which might causeregeneration coupling with other portions of the amplifier, such as theoutput of the amplifier.

In the embodiment shown in Fig. 3, the 460- kilocycle primary andsecondary are preferably located in aseparate shield from the2500-kilocycle primary and secondary windings. It will also be notedthat the high frequency secondary is connected in circuit adjacent tothe input grid of the rst amplifier tube I5, with the low frequencysecondary more adjacent to ground or the bias supply connection.

The switching of the input circuit of the two channels of the amplifiermay be arranged so 1 that no high alternating current or intermediatefrequency potential is provided at the switch terminals, while at thesame time providing for using separate converter tubes for each of thetwo channels, as shown in Fig. 4, to which attention is now directed.

Referring to Fig. 4, the superheterodyne receiving system shown isadapted for receiving signals in two different frequency ranges, one ofwhich is a relatively high frequency range, for example, above 20megacycles. In this system, an intermediate frequency amplifier arrangedfor double frequency response is provided, and comprises two amplierchannels 55 and 56, utilizing common amplifier tubes indicated at 5'Iand 58. .The amplifier tubes are connected in cascade relation throughinterstage coupling transformers indicated at 59, 60, 6I and 62, the rsttwo being tuned to respond to a relatively high intermediate frequency,such as 2500 kilocycles, and the latter two being tuned to respond to alower intermediate frequency, such as 460 kilocycles, for example.

The secondaries of the transformers 59 and 6I are connected permanentlyin series as shown, to form the input grid circuit for the inputamplif'ler tube 51, and the output circuit of the tube 51 includes theprimaries of the transformers 60 and 62, connected in series as shown.The input or grid circuit of the tube 58 is provided by the tunedsecondaries of the transformers Bil and B2, permanently connected inseries. This follows the same arrangement as previously described inconnection with Fig. 1, and places the windings of the higher frequencycoupling transformers in circuit adjacent to the tube elements. The

detector is not shown, but may be coupled as preu viously shown anddescribed in connection with Fig. 1.

'I'he input circuit of the two-channel amplifier comprises a tunedprimary winding 68 for the high frequency transformer 59, and a tunedprimary winding 8| for the low frequency transformer 6I. Each of theseprimary windings is connected to a separate converter or mixer tube, theprimary 88 being connected to the output circuit of a mixer tubeindicated at 55. and the primary winding 64 being connected to theoutput circuit of a mixer tube 55. 'I'his arrangement permits adifferent type of mixer or frequency converter tube to be used for theproductionof the two intermediate frequencies.

For the high frequency channel 55, the converter tube 65 is of the typehaving two control grids indicated at 51 and 58, the first named gridreceiving signals through a iixed tuned band pass filter indicated at68, from a signal source such as an antenna circuit 18, and the grid 58receiving oscillations through a coupling capacitor 1l, from the tunedcircuit 12 of a separate oscillator tube 13.

The converter or mixer tube 88 is of the combined oscillator and mixertype. adapted to provide self-oscillations through the inclusion thereinof oscillator electrodes 1I coupled to a tuned oscillator circuitindicated at 15. Signals are introduced into the tube through a controlgrid 18 and a tuned signal input circuit 11, also coupled to the signalenergy supply circuit 10, as indicated by the tuned primary winding 18.

The three tuned circuits 12, 15 and 11 are arranged to be variably tunedby means of a multiple unit tuning capacitor providing uni-control andcomprising a variable tuning section connected across the circuit 12,' asecond variable tuning section 8| connected across the circuit 15, and athird variable tuning section 82 connected across the circuit 11. 'Iheuni-control operation of the three sections is indicated by the dottedconnection 83.

The low frequency channel 55 of the amplifier receives signals at theintermediate frequency from the frequency converter 55 which convertsthe incoming signals timed in by the circuit 11 under control of thevariable capacitor section 82. The oscillations are introducedelectronically into the electronic stream of the device 55, as is wellknown, and the oscillations are controlled in frequency by the variabletuning capacitor 8| simultaneously with the tuning of the circuit 11,the circuits 11 and 15 being arranged to provide the desired frequencydifference throughout the tuning range of the circuit 11. This type ofoscillator and mixer is suitable for use in connection with lowfrequency circuits such as the standard broadcast and medium short wavebands, and reduces the number of tubes employed and the circuitconnections thereto. In the present example, the tuned circuit 11 may beconsidered to respond to the broadcast band of 540 to 1600 kilocycles,and to produce an intermediate frequency of 460 kilocycles.

The tube 66 is energized under control of a switch 85 in the cathodecircuit indicated at 86, and in the present example is shown in theclosed position, for causing the tube 56 to operate as a converter ofthe detector-oscillator type. When the receiver is operating in the lowfrequency range, the oscillator 13 and the mixer 55 are deenergized bysuitable switching control means, which in the present example comprisesa switch 81 located in the cathode circuit 88 of the tube 65, and aswitch 89 located in the anode circuit 80 of the tube 13.

The switches 81 and 88 are shown in the open position and are arrangedto be open, as shown, when the switch 85 is closed, also as shown, Theswitches 85, 81 and 8! may form sections of a common switch means, andare. in any case, arranged for uni-control operation, as indicated bythe dotted connection Il, whereby. when the switches 81 and 89 areclosed, the section 85 opens, and vice versa.

When the switches 81 and 88 are closed, the oscillator 13 and the mixertube l5 are energized and signals from the oscillator 18 are applied tothe mixer tube 58, to beat with incoming signals on the grid 81,received through the band pass filter 69. If the band pass filter istuned to a fixed frequency band in the range of ultra high frequencies,such as from 40 to 41 megacycles, for example, the tuning of the systemwithin that band may be effected by tuning the oscillator alone by thevariable tuning capacitor section 80, and this arrangement is followedin the present example, although it should be understood that the inputcircuit for the grid 51 may be tuned by uni-control means in the samemanner that the control grid 15 of the mixer tube 56 is tuned by thecircuit 11.

The oscillator 13 is tuned through a. frequency range to beat with theincoming signals through the band pass filter 58, to produce the desiredintermediate frequency of 2500 kilocycles, for example, which passesthrough the channel 55. The channel 55 is rendered ineffective bydeenergizing the converter or mixer tube 55 by the opening of the switchsection 85.

The circuit of Fig. 4 has the advantage that no intermediate frequencypotentials are applied to the switch terminals 81, Il or 85, andprovision is made for utilizing separate converter tubes for each of thefrequency bands, each having advantages not possessed by the other forthe particular use. For example, at ultra high frequencies, ,theconverter tube 85, with separate mixer grids and a separate oscillator,operates with more uniform output and frequency stability than with acombined oscillator and detector tube of the type -shown at 85.

The superheterodyne receiverl circuits herein disclosed include twointermediate frequency channels, one having characteristics suitable foruse in connection with reception of radio frequencies in the order of1000 kc. and 10,000 kc. having channel allocations with approximately 10kc. separation, and the other one having characteristics suitable foruse in connection with reception of radio frequencies in the order of50,000 kc., for example, having channel allocations with about 50 kc.separation.

Means are provided for combining the two in termediatefrequency channelsinto one cascade amplier employing common intermediate frequencyamplifier tubes, with selecting means, restricted to the input circuitspreceding the iirst intermediate frequency amplifier tube, resonant foreffectively passing only signals in one or the other of the intermediatefrequency channels.

I claim as my invention:

l. An intermediate frequency amplifier system for multiple wave bandreceivers, comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher. intermediate frequencyfalllng between two of the harmonics of the lower intermediatefrequency, and a plurality of amplifier tubes connected to operatejointly with both of said channels.

2. An intermediate frequency amplier system for multiple Wave bandreceivers, comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher intermediate frequency fallingbetween two of the harmonics of the lower intermediate frequency, aplurality of amplifier tubes connected to operate jointly with both ofsaid channels, means providing selective input circuits for saidchannels resonant for passing signals at said lower and higherintermediate frequencies, and wave band change means having an elementmovable to select one of said input circuits.

3. An intermediate frequency amplifier system for multiple wave bandreceivers comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher intermediate frequency fallingbetween two of the harmonics of the lower intermediate frequency, aplurality of amplifier tubes connected to operate jointly with both ofsaid channels, and means for introducing an intermediate frequencysignal into each of said channels selectively at the input ends thereofcomprising a selector switch, and means providing wave band changecontrol for operating said selector switch.

4. An intermediate frequency amplifier system for multiple wave bandreceivers comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher intermediate frequency fallingbetween two of the harmonics of the lower intermediate frequency, aplurality of amplifier tubes connected to operate jointly with both ofsaid channels, and means for introducing an intermediate frequencysignal into each of said channels selectively comprising a tuned inputcircuit for each channel resonant for effectively passing only signalsat the lower and the higher intermediate frequencies, a selector switchconnected with said input circuits for rendering one or the othereffective to respond to signals, and means providing wave band changecontrol for operating said selector switch.

5. In a superheterodyne receiver, the combination of means providing twointermediate frequency signal channels, tuning means in one of saidchannels for passing intermediate frequency signals in a narrow lowerfrequency band and tuning means in the other of said channels forpassing signals in awider and higher frequency band lying between twoadjacent harmonics of the mean frequency of the lower frequency band,circuit means including common amplifier tubes for combining the twointermediate frequency channels into one cascaded amplifier circuit,means providing selectable tuned input circuits for each of saidchannels preceding the first intermediate frequency amplier tube, saidcircuits being resonant and selective for effectively passing onlysignals in one of the intermediate frequencies through said ampliercircuit.

6. An intermediate frequency amplifier system for multiple wave bandreceivers, comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher intermediate frequency fallingbetween two f the harmonics of the lower intermediate frequency, aplurality of amplifier tubes connected to operate jointly with both ofsaid channels, and means for introducing an intermediate frequencysignal into each of said channels comprising a sepalate converter tubeand means for selectively energizing said tubes.

7. An intermediate frequency amplifier system for multiple wave \bandreceivers, comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels one to a lower andthe other to a higher intermediate frequency, the higher intermediateirequency falling between two harmonics of the lower intermediatefrequency, a plurality of ampliner tubes connected with said last namedmeans to operate jointly with both of said.channels, means forintroducing an intermediate frequency signal into each of said channelscomprising a frequency converter for each channel, a tunable highfrequency oscillator coupled to the frequency converter for the higherintermediate frequency channel, means for introducing signals within apredetermined high frequency band into the last named converter, meanstunable conjointly with the high frequency oscillator for introducingsignals and oscillations into the other of said converters, and meansfor selectively energizing said last named converter with respect toenergization of the first named converter and oscillator.

8. An intermediate frequency amplifier system for multiple wave bandreceivers, comprising means providing two intermediate frequencyamplifying channels, means for tuning said channels one to a lower andthe other to a higher intermediate frequency, the higher intermediatefrequency falling between two harmonics of the lower intermediatefrequency, a pluralityof amplifier tubes connected with said last namedmeans to operate jointly with both of said channels, means forintroducing an intermediate frequency signal into each of said channelscomprising a tube having two signal input grids and output circuits, onecoupled to each of said channels to provide separate frequency convertermeans for said channels, a tunable high frequency oscillator coupled toone of the input grids of the converter tube for the higher intermediatefrequency channel, means for introducing signals within a predeterminedhigh frequency range into the last named converter tube connected withthe other of the signal input grids thereof, means tunable conjointlywith the high frequency oscillator for introducing signals andoscillations into the other 'of said converter tubes connected with oneof ,the signal input grids thereof, and means for selectively energizingsaid last named converter tube with respect to energization of the firstnamed converter tube and oscillator.

9. In a superheterodyne receiver, means providing a multiple wave bandtuner and oscillator, tuning control means therefor, wave band changecontrol means therefor, and an intermediate frequency amplifierproviding two intermediate frequency amplifying channels therein and aseries .of cascaded amplifier tubes common to and connected with bothsaid channels jointly, one of said channels having frequency responsecharacteristics for the reception of signals in the tuning means andoscillator in a frequency range below 10,000 Akilocycles with signalchannel allocations permitting approximately 10 kilocycle separation andthe other of said channels having response characteristics for thereception of signals in the tuning means and oscillator in a frequencyrange above 10,000 kilocycles with signal channel allocations permittingfrom 10 to 50 kilocycle separation, means providing selectable tunedinput circuits for said channels preceding the rst intermediatefrequency amplier tube, said circuits being selectable and resonant foreffectively passing only signals in one or the other of saidintermediate frequencies to which the separate channels are responsive.

10. In a superheterodyne receiver, the combination of means providingtwo intermediate frequency signal channels, tuning means in one ofsaidchannels for passing intermediate frequency signals in a narrow lowerfrequency range and tuning means in the other of said channels forpassing signals in a wider and higher frequency range lying between twoadjacent harmonics of the mean frequency of the lower requency range,circuit means including common amplifier tubes for combining the twointermediate frequency channels into one cascaded amplifier circuit,means providing selective tuned input circuits for each of said channelspreceding the first intermediate frequency amplifier tube, said circuitsbeing resonant and selective for effectively passing only signals in andthrough one of the intermediate frequency amplifying channels to theexclusion of the. other, said last named means including a highfrequency tuned secondary winding and a low frequency tuned secondarywinding of two separate intermediate frequency coupling transformersserially in the input circuit of the rst intermediate frequencyamplifier tube, a tuned primary Winding for each of said transformers,and means for selectively detuning the high frequency primary windingand the low frequency secondary winding concurrently with selectivechange in the tuning response of said receiver.

11. An intermediate frequency amplier system for multiple wave bandreceivers, comprising means providing two intermediate frequnecyamplifying channels, means for tuning said channels to a lower and ahigher intermediate frequency, the higher intermediate frequency fallingbetween two of the harmonics of the lower intermediate frequency, and aplurality of amplifier tubes each connected with both of said channelsto operate jointly therewith, and means responsive to wave band changefor selectively applying signals at said intermediate frequencies tosaid channels.

12. In a multiple wave band superheterodyne receiver, the combination ofmeans providing two intermediate frequency signal channels, tuning meansin one of said channels for passing intermediate frequency signals in anarrow lower frequency range and tuning means in the other of saidchannels for passing signals in a wider and higher frequency range lyingbetween two adjacent harmonics of the mean frequency of the lowerfrequency range, circuit means including common amplifier tubes forcombining the two intermediate frequency channels into one cascadedamplifier circuit, and meansproviding selective tuned input circuits foreach of said channels preceding the first intermediate frequency ampliertube, said input circuits being resonant and selectable in response tochange in wave band for effectively passing signals in each of theintermediate frequencies selectively through said amplifier circuit.

13. In a superheterodyne receiver, the combination of means providingtwo intermediate frequency signal channels, tuning means in one of saidchannels for passing intermediate frequency signals in a narrow lowerfrequency range and tuning means in the other of said channels forpassing signals in a wider and higher frequency range, circuit meansincluding common amplifier tubes for combining the two intermediatefrequency channels into one cascaded amplifier circuit, means providingselective tuned input circuits for each of said channels preceding thefirst intermediate frequency amplifier tube, said circuits beingresonant and selective for effectively passing only signals in andthrough one of the intermediate frequency amplifying channels to theexclusion of the other, said last-named means including a high frequencytuned secondary winding and a low frequency tuned secondary winding oftwo separate intermediate frequency coupling transformers serially inthe input cir- Y cuit of the rst intermediate frequency amplier tube, atuned primary winding for each of said transformers, and means forselectively detuning the high frequency primary winding and the lowfrequency secondary winding concurrently with selective change in thetuning response of said receiver.

14. In a multiple wave band superheterodyne receiver, the combination ofmeans providing two intermediate frequency signal channels, tuning meansin one of said channels for passing intermediate frequency signals in anarrow lower frequency range and tuning means in the other of. saidchannels for passing signals in a wider and higher frequency range,circuit means including common amplier tubes for combining the twointermediate frequency channels into one cascaded amplifier circuit, andmeans providing selective tuned input circuits for each of said channelspreceding the first intermediate frequency amplifier tube, said inputcircuits being resonant and selectable in response to change in waveband for effectively passing signals ineach of the intermediatefrequencies selectively through said amplifier circuit.

WENDELL L. CARLSON.

